Apparatus for heating and cooking



July 3, 1945. B ELMR 2,379,509'

APPARATUS FOR HEATING AND COOKING Filed Jan. l2, 1939 '3 Sheets-#Sheet lmem/tom MMM July 3,' 1945. W B ELME-R 2,379,509

APPARATUS FOR HEATINGv AND COOKING Filed Jan. 12,' 1959 5 Sheets-Sheet 2ELECTRIC Y UPPLY WILLIAM B. ELP/IER July 3, 1945. w B. ELMER 2,379,509

APPARATUS FOR HEATING AND COOKING Filed Jan. 12, 1939 5 Sheets-sheet sf5 r L ELECTRIC J SUPPLY 75` NIU- IAM ENELMER Patented July 3, 1945UNITED STATES4 PATENT oFFlcE APPARATUS FOB HEATlNG AND CQQKlNG WilliamB. Elmer, Winchester, Mass.

Application'January 12, 19,39', yserial No. 250,562

2 claims. (c1. 21e-20) The present invention relates to the control ofelectrical heating systems, and more particularly to an apparatus forcontrolling electrical heating systems used primarily for domesticstoves or ranges and the like.

Domestic electric stoves or ranges usually are provided with electricalheating units of the exposed or surface type over which pots, pans orother receptacles for containing food, or the like,

are adapted to be placed. It has been common practice to control theheat emitted from such units by switches which connect the sources ofelectrical energy to the electrical resistance elements of the units invarious combinations to obtainfseveral heating stages; Generally, therehave been provided but three predeterminedsettings, namely, low,* mediumand high, thus greatly limiting the selectivity with which the heatingunits may be controlled. It has also been the practice to usethermostatic temperature-responsive control devices for maintaining theheating units at a predetermined temperature. These devices act toopenthe circuit when a predetermined temperature has been reached and toclose the circuit when the temperature has `fallen below the'desiredtemperature. Such devices are unsatisfactory because variations insurrounding air currents or ambient temperatures or the type of cookingutensil utilized impair their accuracy.

The present invention aims to overcome the above objections by providinga heating control system 4having a pair of lheating elements,a one of iwhich is associated with an adjustable thermostatic switch forselectively varying the average rate of heat emitted therefrom in smallincrements to adjust the temperature over a wide range, for example,from initial heating temperature of such element, to its maximum heatingtemperature, the system further having manually operable switch-means,-preferably associated with the control member for adjusting thethermostat, to connect both ofthe elements to the Vsupply source andrender the thermostatic switch ineffective to govern the power of supplyto the element with which it is associated.

My improved system has various advantages among which may be mentionedthat like controllers having a single standard current rating may beemployed in connection with the several heating units of-a cooking rangehaving a variety of ratings; the intermittent vconnection ofthe entireelectric load of 'a-single large heating unit tot the electricalv supplycurrent is avoided and thus-undesirable fluctuations in the voltage ofthesupply systemA is prevented; and the heating elements may becontrolled in such manner as to effect economical cooking.

A further object is to provide an electrical heating system which ispositivev in operation and utilizes a minimum number of parts, is sturdyin construction,` is simpleand economical to manufacture, and effectsv asaving of electrical energy.

Other objects will be in'part obvious and in part pointed out more indetail hereinafter.

The'invention accordingly consists inthe features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereafter set forth and the scopeof theapplication of which will be indicated'in the appended claims.

'In the accompanying drawings:

Fig. 1 is a top plan view of a thermostatic controlling device adaptedto vbeutilized in my improved system;

Fig. 2'is aside view of the devicelillustrated in Fig. 1;

Figs. 3A and 3B are isometric exploded views of the device shown inFigs. 1 and 2;

Fig. 4 is a fragmentary perspective view showing the device in assembledposition relative to the operating panel of an electric range;

Fig.v 5v is a vwiring'dagram showing several heating units of anelectric range controlled by the present apparatus, the heating unitsbeing adapted to' be operatively connected to a three or four wireelectrical supply line;

' Fig. 6 is a wiring diagram illustrating a heating unit having a pairofresistance elements electrically connected to a two wire electricalsupply line.

Referring to the drawings, in Figs. l toy 3B, I have shown, forillustrative purposes, a controlling device liwhich may be utilized inmy mproved system, the same being like that disclosed in my UnitedStates Patent No. 2,182,048 issued December 5, 1939; The device has amanually operatedknob l2 adjacent a control panel i3 (Fig. 4) at thefront wall'lli yof the rangeand secured .to a shaft or rod l5operatively connected to the control device.

The heating. unit control device Il preferably ismounted in asuitablerectangular protected casing IB (Fig. 4) adapted to shield itfrom air currents, and heat radiated rby the heating unit. vThe top ofthe'casin'g may be`open and a suitable Ventilating screen member Ilmaybe placed over the top, The casing has a front Wall I9 on whichtherev is mounted, but insulated from, a` pair Aof posts 20 and 2|,wh'chproject 'forwardly of the wall I9 and serve as vterminals forvelectrical 'connections 24 and 25 to the heating element which thethermostatic switch is arranged to control, and which element isdesignated by the letter A in Fig. 5 and by the letter B' in Fig. 6. Theposts and 2l project inwardly from the wall to respectively support andbe electrically conn'ected to the forward legs 26 and 21 (Figs. 1 and 2)of composite inverted U-shaped bi-Inetallic strips 28 and 29. The rearlegs 30 and 3| of the composite strips 28 and 29 are interconnected by,but insulated therefrom, a strip providing a relatively fixed supportfor a thermostatic responsive motor element 3S adapted to deect andreturn in response to the flow of electrical current. In the embodimentillustrated, the element 36 is also in the shape of an inverted U withthe rear leg 39 thereof secured to, but insulated from, the strip 35 bythe rivets 40. The forward leg 4I is free to float forwardly andrearwardly upon changes of temperature in the thermostatic motor element36. The compensating strips 28 and 29 are equivalent in thermostaticaction to the motor element 36 and serve to compensate for variations tothe ambient temperatures, for example, surrounding air temperatures;whereby the floating leg 4| of the motor element 36 will always be inthe same relative position to the supports 2D and 2| when it is notacting in response to the flow of current. The motor element 36 consistsof a relatively wide strip of suitable conducting material subdividedlengthwise, without effecting its stiffness and deflection, into a gridhaving a plurality of narrowjbars (Fig. l) alternately joined at theiropposite ends to form a tortuous path of greater electrical resistanceto the heating current than to be offered without the subdivisions.Preferably, an element constructed and supported in the above/manner isutilized because the dissipated heat thereof may be readily carried olf,though any other suitable element may be used.

The fixed leg 39 of the motor element has a downwardly depending finger46 which is electrically connected, through a relatively thin copperstrip 41, to a depending finger 43 of the compensating strip 28. Theamount of current passed through member 28 will be relatively small andinsuicient to affect its compensating for ambient temperatures. Theforward oating leg 4I of the motor element 36 has a depending finger 50electrically connected through a copper strip 5| to the depending finger52 of a plate 54 which is carried by, but insulated from, the motorelement leg 4I and in turn carried a contact 55. There is also carriedby, but insulated from, the leg 4I of the motor element a U-shapedabutment member 56 having its forward leg 51 in alignment with butspaced forwardly from the contact whereupon, as the free leg 4| of themotor element floats forwardly and rearwardly, it carries therewith thecontact 55 and U-shaped abutment member 56 which being fixed relative toone another maintain a set distance therebetween.

Positioned forwardly of the motor element 36 is a snap acting member 6Uwhich carries adjacent its lower end, an electrical contact 6I having abackspacer 62; which Contact and spacer are positioned intermediate ofthe forward leg 51 of the U-shaped member 56 and the contact member 55of the motor element 36 and when so positioned are interengaged andadapted to cooperate therewith to intermittently open and close thecontacts 55 and 6I.

.'Ihe snapping or flexible spring element 60 has a plurality of inherentcurvatures about different axes and is adapted to snap from one positionof stability to another and, as illustrated, is provided with a centralaperture 63 through which depends a supporting tongue 65 (Fig. 2). Thetongue 65 in turn is mounted on the inner end of a post Bil which issecured to the front wall |51 of the heating unit casing, therebyproviding a fixed center about which the snap spring may be flexed.

The inherent curvature or the snap acting spring relative to its supporton the post 66 may be varied by rotation of the manual operable knob lilas about to be described. Preferably, the shaft lli is threaded forrotation into the front wall I3 of the heat controlling device casingand its inner end is provided with an abutment lll of insulatingmaterial adapted to engage the snap spring. The shaft i3 is so supportedthat its abutment I0 is offset from the center of the snap actingspring, preferably above the center, so that upon rotation of the knob,the shaft may be moved inwardly and outwardly and the abutment "FIJvaries the strain upon the spring 66, thereby flexing it relative to itsfixed center and changing the inherent curvature thereof. By varying thepoint to which the spring will flex from one positionoi' stability toanother, the ratio of `the time during which the contacts are open, ineach cycle ol' operation, is adjusted.

The outer end of the post 66 for the spring 60 is electrically connectedto a source of power, and, when the spring is flexed to a position ofstability where the contacts and 6I are closed, the current will fiowfrom the post 66 through spring Gil and through the closed contacts 55and 6i to the motor element 36 then through the compensating strip 23and post 20 to the heating unit connection 24. The circuit for theheating unit is completed through post 2| which is provided with aninwardly projecting member 12 adapted to be engaged by the auxiliarycontact at the lower end of an arm 14, which arm is supported at itsupper end by the inner end of a terminal or post 15. The post 15 issupported on, but insulated from, the wall I9 and has its outer endconnected to the source of power.

The operation of the switch arm 14 is also controlled through the shaftI5 which carries thereon a disc 16 of suitable insulating material whichis secured to the shaft by a lock-nut 11. The disc "I6 has a projectingarm 19 adapted to engage an inwardly projecting ear of the contact arm14 to move the contact arm to open positicn and the ear is adapted toexert pressure on the arm I9 to hold it at its limit of travel therebyserving to secure the shaft I5 in position.

The knob I2, at the forward or outer end of the shaft l5 is providedwith a pointer BI cooperating with indiciaon the control panel I3 togive a visual indication of the setting of the controlling device. Forexample, when the knob pointer is aligned with the off position 84 onthe panel, the arm 19 will engage and hold the switch arm uI4 in openposition and the abutment 16 will so bear against the spring 60 that itiS in the position shown in Fig. 1, with contacts 55 and 6I open andspaced apart approximately twenty-thousandths of an inch. rl'his spacinghas been found desirable if the device is to be used on alternatingcurrent. Upon rotation of the shaft I5 to the on position 85, the arm 19will initially allow the closing of the switch arm 14 to complete oneconnection to the heating unit and the abutment 10 will' then place thespring 60 under sufficient strain to cause it to snap over dead centerfrom one position of stability to another and close contacts 55 and 6|thereby completing the other connection to the heating unit.

As the motor element 36 becomes heateddue to the current flowingtherethrough, the forward leg 4| thereof, will move forwardly with thecontacts 55 and 6| in wiping engagement until the spring 6D is againflexed over dead center and into engagement with the abutment member 56.The circuit will then remain broken until the motor element 36 cools andthe abutment member 56 is carried rearwardly to a point where the spring60 again flexes to cause the contacts 55 and 6| to engage.

The amount of time elapsed between the ope ing and closing of thecontacts 55 and 6| may 'be selectively varied in small increments byfurther rotation of the knob l2 in a clockwise direction to cause theabutment l to increase the strain to which the spring 60 is subjected.As the knob is rotated in a clockwise direction and the strain isgradually increased, the contacts 55 and 6| remain closed for a longerperiod of time while the motor element 36 deflects to meet the new deadcenter position of the snap spring 66 at which time `the cycle ofalternate opening and closing of the contacts 55 and 6| is resumed. Aspressure on the upper end of the snap spring 50 is increased by inwardmovement of the abutment the lower end of the snap spring carrying thecontact member 6| is moved outwardly towards the forward leg 51 of theabutment member 29 to establish tension in the spring 6i! ytending toshorten the total time cycle of operation. For example, when the knobpointer is advanced to substantially the midpoint between on and offjthe cycles of operation are shortest in over-al1 time. When the abutment'l0 on the shaft is advanced beyond the dead center position of the snapspring the operating cycles again increase in total duration with the onportions of the cycle becoming longer and the off portions shorter untila point is reached where the strain on the spring prevents deflectionthereof by the leg 4| during continuous ilow of current through themotor. In this manner, there is provided a complete range of controlwith an innite number of positions from initial heating to maximumheating capacity of the heating unit.

` In order to prevent heat loss `through the motor element when theheating unit is operated at its capacity load, there is further:provided a cut-out switch. This switch may comprise a second auxiliarycontact having a resilient switch arm 8l, controlled by the arm 1B onthe shaft |5, and electrically connected to the post 66 at itsl upper'end, and having its lower enid lpositioned to engagea member 89projecting inwardly from the post The arm 19 is adapted to engage theswitch arm BI and close the circuit when the knob pointer is turned tofull, and thus `short circuit, or shunt, the motor element 36, byestabilishing a circuit from post 66 through arm` 8'! to post 26, thento the heating element il), and from theheating unit to the post 2|, andthrough switch arm 'M to the post 15. The switch varm S1 is alsoprovided with an inwardly projecting' ear 49|) adapted to engage the arm19 to hold it inset position. If it is desired tobring: the heating unitto 4a high temperature -in a/.relatively short time, the arm 19 maybeturned to full position, thus short circuiting the grid of the motor andhaving the usual effect of a double pole switch device.

In order to obtain more efficient operation; there may be provided ashield 9| intermediate the grid and the compensating members 28 and 29to prevent radiation of heat from the grid affecting the compensatingmembers.

Figs. 5 and 6 diagrammatically illustrate the controlling device asbeing embodied in my improved system. In such instance, as will be seenfrom these Figs. 5 and 6, the controlling device has an additionalauxiliary switch 8l' whereby the heating element which is not controlledby the thermostat may be connected to one of the lines oi the source ofsupply. In Fig. 5, an arrangement is shown wherein two surface heatingunits of an electric range are each provided with a heat controllingdevice, In this instance, the 4cut-out switch 'lli is omitted, and thecontrolling devices are shown as each having a, shunt switch M* and `anauxiliary switch 81. In Fig. 6, a two-element heating unit is shown,andthe controlling device is shown as having the cut-out switch i4 andthe switches` 81 and 81.

Each of the heating units shown in Fig. 5 consist of two individualheating elements, designated as A and B in one case and as A and C inthe other` case. It will be observed .that the circuit designated as Ain each case is controlled through element 36 of the intermittent heatcontroller il as described. The second and outer circuit, designatedvariously `as B yand C is not subject to the intermittent heat controldescribed, but remains steadily connected or dis connected to theelectric supply circuit depending upon the position of `the operatinghandle and the cam of the switch 8l. electric ranges to provide aplurality of sizes of surface heating units, such as` 60G, 1000, i200,and 2000 watts, for example. If single circuit heat ing elementsy insuch variety of ratings were used, the heating currents in the variouscontroller elements would be dissimilar, and it would then be necessaryto providein each electric range a variety of controllers each havingarating,correspond ing to the current rating of its controlled heatingunit. This condition would impose practical difficulties in stocks ofspare parts and in range wiring connections which would be troublesomein practice. In order to avoid this diiiiculty, and to make possible theuse of a `controller having one `single standard current rating, theheating units have been subdivided in some cases into two circuits, asA-B and A-C", in which case one heatingl circuit of every heating unit Adraws a like amount of electric current from the electric supply. Inthis case, the regulating devices 36 can lbe identical although .thetotal watt capacity of the several heating units may be considerablydifferent, one from. the other.

A `second advantage in subdividing the heating units into two heatingcircuits is in the fact that the intermittent connection of the entireelectrical load of a sinlgle large heating unit to the electrical supplycircuit is thereby avoided. Such in termittent connection of a largeload would otherwise produce fluctuations in the voltage of someelectric supply Isystems which would cause ob'- jectionalble flicker ofelectric lamps also connected to said supply.

Yet another advantage is that in most cooking operations, it is nrstnecessary to apply a maximum of heat to raise the cooking vutensil to Itis customary in y switches 14 and 81.

a boiling or cooking temperature, after which it is necessary only tomaintain the same utensil at a boil, which requires a substantialreduction in the amount of heat originally applied. Ii regulation ofheat were made availalble over the full range of heat from very low heatup to the maximum ol heat availaible from the largest heating unit onthe range, it would be possible for careless cooks to allow the controlto remain at high intermediate heat adjustments near the maximum heatwhich would be wasteful ol heat and result in uneconomical cooking. Inthe present system, when the heat is turned down in the largest units,there is an abrupt decrease in heating rate from the maximum available,to approximately that amount which is normally required to maintaincontinuous cooking in the cooking utensil. The watt ratings of the twocircuits in each unit may be selected to meet this requirement to `thebest advantage.

In Fig. the regulated coil A occupies a control location within theunregulated coil B' or C'. This arrangement provides for the mosteconomical use of low heat adjustments, since the outer edge of theheating unit will then operate relatively cool, and a greater proportionof the total heat will be transferred through the cooking vessel proper.Another advantage of the arrangement described, is :that smaller cookingutensils, normally requiring less total heat for cooking, may be usedefliciently over the inner heating circuit, Whereas with all older typesoi" surface heating unit control commonly used in. electric ranges, thelowest heats have been distributed over the entire heating unit surface,requiring a large utensil for enonomical cooking.

In Fig. 5, one terminal of each heating coil 'ci' oach'heating unit isconnected to the N or neutral supply wire, and the opposite terminals oithe several Luiits are disposed among the live wires A, B and C in suchmanner as to diversify the electric load among said wires A, B and C. Itwill be noted that two circuits are connected to wire A, two othercircuits are connected to wire B and the iiith circuit to wire C. Theadvantage ol .this arrangement is that the three heating units areconnected to different phases` of the supply system to preventoverloading.

li desired, the four wire supply system may be operated as a three `wiresingle phase system. This may be accomplished Iby connecting the wires Band C together, connecting one :terminal ol' the heating units to wire Aand connecting the other terminal of the heating unit through thecontrol device to the wires B and C. When lthe supply line is used inthis manner, the wire N may be used as a neutral or ground wire.

Referring now to the embodiment shown in Fig. 6, a heating unit is shownas having an outer element B adapted to be controlled loy thethermosta't, and an inner element C adapted to be connected to `theelectric supply through the 'Ihe switch 14 is in the connection lleadingto corresponding ends of the heating elements and functions as a lineswitch. The switch 81 corresponds in operation and function to theswitch 81 shown in Figs. l and 2; namely, it directly connects theresistance B' to a supply line when the knob l2 is turned to its maximumheat position and thus shunts the thermostat. The centrally locatedswitch 81' may :be a duplicate of the vswitch 8l but is associated withthe other resistance C so as to cut that resistance into circuit whenthe knob is turned to maximum heat position.

The operation of the arrangement shown in Fig. 6 is briefly as follows:When the parts are in their oil positions, all supply is interrupted,that is, the control or threaded rod I5 is in backed-oli` position sothat the snap action member 6U maintains an open position and all of thecam operated switches are open. In this position, the pointer oi" theknob will `be pointing downwardly, referring to Fig. 6. Upon turning thecontrol rod `from its oil position, line switch ld is closed to completeone connection to the heating elements, and the control rod will thenplace the snap action spring 60 under sufficient strain to cause it tosnap over dead center to a closed position where the contacts 55 and 6|engage, thus completing the connection through the heating element B.The heating element B' is now under the control of the thermostat, theswitch ill and the switch 81 both being open, and by suitably adjustingthe control rod, the time interval during which the thermostaticallyoperated switch remains open and closed may be regulated.

When the control rod is turned to adjacent its full on position, shownin Fig. 6, the thermostatic switch 55, tiy is Vmaintained closed becausethe control rod has reached a point where it will prevent deiiection ofthe spring Sil and thus the thermostatic switch is rendered ineffectiveto regulate the average power delivered to the resistance At this time,the switch 8l is closed so as to shunt the thermostatic switch and tocontinuously connect the resistance B to the supply lines.llurtherniore, at abollt the Same time the switch is closed, the switch8l is closed so that the other resistance C is now energized wherebylboth of the resistances simultaneously generate heat in the hot plateto provide a constant maximum heat output to the plate.

llrom the foregoing description, it will be seen that the presentIinvention provides an improved method and system for controllingelectrical heating units adapted for domestic ranges and the ihe averageamount of heat is accurately and economicallycontrolled, and an infinitenumber oi adjustments may :be made between the initial and the maximumheating capacity of the heating units without substantial loss ofelectrical energy. llhe heating units, when set to emit a predeterminedaverage amount of heat are adapted to heat or cook foods more unii'ormlyand preserve their flavor and nutritive value. The system and controldevices are simple and inexpensive in construction, can be economicallymanufactured, and readily installed lboth in new and existing ranges.The control devices are suitable for any oi electrical supply, arerugged in construction, and can readily withstand any rough usage towhich they may be subjected.

As many changes could be made in the above construction and manyapparently Widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the followingclaims is intended to cover all of the generic and specific features ofthe lnvention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

I claim as my invention:

1. In a heating system having a pair of heating resistances and anelectrical supply source for said resistances, means for controllingsaid resistances comprising a thermostatically operated timing switchand a master switch, the latter operating through said thermostaticallyoperated switch in a series of positions to connect one only of saidresistances to said supply source and in another position to connectboth of said resistances to said supply source, said thermostaticallyoperated switch being rendered ineffective to govern the power supply tosaid resistances when said master switch is in said other position andrendered effective to control the average power supplied to said oneresistance when said master switch is in any one of said series ofpositions and supply diilerent average powers to said one resistance foreach of said series of positions.

2. An electric hot plate heating system comprising a pair of heatingresistances, an energizing circuit for said resistances, rst and secondswitches, a thermostat connected to said rst switch to ope'rate itbetween its opened and closed positions, a. manually operable controlmember connected to said thermostat and to said second switch operatingwhen moved from an off position to cause said thermostat to operate saidrst switch to close to energize one of said resistances,

while said second switch remains n its open position so that said otherresistance remains deenergized, means for heating said thermostatcontrolled by said iirst switch so as to apply heat to said thermostatwhen said switch is closed to raise the temperature of said thermostatto cause it to operate said iirst switch to its open position in a timedinterval, whereupon it shuts off the heat from said thermostat to permitto cool to return said first switch to its closed position in a timedinterval to reenergize said one resistance, whereby the average powersupplied to said one resistance is regulated, said manually operablecontrol member controlling said thermostat when operated through apredetermined range of movement beyond said off position to vary saidtimed intervals and thereby said average power supplied to said oneresistance, and when operated to a position beyond said range to controlsaid thermostat to maintain said iirst switch in its closed positionirrespective of the operation of said heating means so that said oneresistance is continuously energized, and also when operated to saidposition said control member operates said second switch to its closedposition to energize the other of said resistances, whereby both of saidresistances simultaneously generate heat in said hot plate to provide aconstant maximum heat output to said plate.

' WILLIAM B. ELMER.

